Ncert Exercises & Solutions

Eukaryotic cells have organelles which may

1. not be bound by a membrane

2. bound by a single membrane

3. bound by a double membrane

Group the various sub-cellular organelles into these three categories

(a) Cell organelles with no membrane In eukaryotic cell, ribosomes occur freely in the cytoplasmic matrix and are attached to the outer cytoplasmic surface of the rough endoplasmic reticulum and nuclear envelope. The ribosomes are also found in the matrix of mitochondria and stroma of plastids called as mitoribosomes and plastidoribosomes, respectively.

(b) Cell organelles with single membrane A lysosome a tiny sac bounded by a single unit membrane of lippprotein. the lysosome occurs in all animals cells and protozoans, prokaryotic cell lack lysosomes.

Number of lysosomes varies with the cell type. Lysosome containa dense, finely granular fluid consisting of glycoproteinaceous hydrolytic (digestive) enzymes called acid hydrolases. Cell organelles like sphaerosomes and microbodies also possess single membranes.
(c) Cell organelles with double membrane Mitochondria are double membrane bound Structures with the outer membrane and inner membrane dividing its lumen distinctly into two aqueous compartments.
The inner compartmentis called the matrix whereas the outer membrane forms the continuous limiting boundary of the organelle. Chioroplast and nucleus are also double membrane bound organelles.

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